Thanks to the spread of electric vehicles, the quantity of batteries produced has increased sharply in recent years. It is therefore necessary to improve the performance of existing batteries, through an optimal management that considers aging models, and the performance of future technologies, through the development of new cell materials. To achieve these objectives, RSE approached the analysis of battery aging from the broadest possible point of view. For this purpose, an aging analysis methodology has been developed which integrates different approaches and aims to pursue both of the aforementioned improvement objectives. The methodology is based on the parallel execution of non-destructive aging tests and destructive post-mortem analyses on batteries based on the same technology, but of different sizes.
The following report describes the results of non-destructive aging tests carried out on NMC pouch-type lithium-ion cells and modules. The cells under test were subjected to 2500 cycles equivalent to and a calendar year and a half of aging tests, under operating conditions characterized by different stress factors. Some cells reached end-of-life conditions, corresponding to a 20% loss of capacity, while others, subject to less stressful working conditions, did not.
The results of the tests were used to define the parameters of an aging model capable of predicting the operational life of a cell or a battery even in working conditions characterized by the simultaneous presence of different stress factors. This model was validated on cells subjected to various stress factors; the maximum useful life estimation error is less than 3%.
The document also reports the design of the database into which the results of the aging tests will be inserted and which will be populated with experimental data.
At the same time, the post-mortem analysis procedure of the cell materials was tested. The half-cells were subjected to electrochemical characterization and aging tests. The results made it possible to highlight critical issues in the test procedure, preventing conclusions on the degradation of the materials from being drawn. The procedure will then be improved before carrying out new tests.